Blue opal is a common opal found in Peru and parts of the US. It's milky in appearance and may include rock matrix. It does not show color play or opalescence, but the blue color is often quite lovely.
Boulder opal is exclusive to opal-rich fields in western Queensland, Australia. It is a thin film of precious opal over an ironstone matrix, a dark stone, giving the stone the appearance of black opal but at lower cost. Boulder opals are often found in freeform shapes to optimize the distribution of opal and its appearance in the dark matrix. Color play is common and striking in these stones.
Fire opal is known for its vivid red-orange body color rather than color play. Fire opal can be milky to transparent, and generally, the more transparent a stone is, the more valuable it is. Mexico is the primary source of fire opals, but they are also found in Australia, the US and Canada.
White and blue precious opals show good color play and opalescence. White opal tends to be a light colored stone with a nice glow and flashes of bright color. Blue opal is similar though with a blue base color. Australia is the primary source, but they are also found in the US, Brazil and Ethiopia.
Peruvian opal is also known as Andean opal and comes from regions of the Andes mountains in Peru. It is a translucent blue-green stone with black dendrite inclusions, giving it terrific pattern. It lacks color play but has plenty of color; trace amounts of copper and chrysocholla are responsible for the bright blue color. It's gained popularity in recent years, and it's common to find Peruvian opal dyed to enhance color.
Pink opal is a common opaque opal with charming soft pink color resulting from a mix of opal, palygorsite and chalcedony. It is found in the Andes mountains as well as Australia.